docs: def _cartesian_to_spherical(cls, coord, center):
          """Cartesian to Spherical conversion
  
          .. warning:: The spherical form is equatorial, not zenithal
          """
          x, y, z, vx, vy, vz = coord
          r = np.linalg.norm(coord[:3])
          phi = arcsin(z / r)
          theta = arctan2(y, x)
  
          r_dot = (x * vx + y * vy + z * vz) / r
          phi_dot = (vz * (x ** 2 + y ** 2) - z * (x * vx + y * vy)) / (r ** 2 * sqrt(x ** 2 + y ** 2))
          theta_dot = (x * vy - y * vx) / (x ** 2 + y ** 2)
  
          return np.array([r, theta, phi, r_dot, theta_dot, phi_dot], dtype=float)